Many doors of contemporary manufacture are formed from hollow channel sections. The channel sections may be extruded aluminum or vinyl, or formed of steel. Such doors have been provided with a latch mechanism to lock the door. Typically the latch mechanism is mounted inside the hollow channel with a hook or latch element which extends through an opening in the edge face of the channel. The latch mechanism has been mounted to the stile by a pair of machine screws which extend through the channel and thread into a flange which is part of the latch mechanism.
Prior art latch mechanisms have been actuated on the interior side of the door by a rotatable lever mounted to an escutcheon or similar plate on the interior face of the door. The lever rotates a tang, and the tang, in turn, extends through an opening in the interior face of the hollow stile and then into a hub which is part of the latch mechanism. Rotation of the lever causes the tang to shift the latch element between extended and retracted positions.
In the prior art, when a key lock has been added to such a door, the tumbler mechanism has been mounted so that a tang projecting from the back of the tumbler assembly is coaxial with the tang extending from the manually operated lever. For many handle designs, especially those where the handle mounts to the escutcheon at a pair of mounting points and where the interior actuating lever is to be midway between the two handle mounting points, this has required the tumbler assembly to be mounted in a housing which projects outward from the stile on its exterior surface. In this location the tumbler assembly is open to attack by those seeking unauthorized entry, and it is in a position which may be awkward for the operator because it may be surrounded by a door handle.